The present invention relates generally to vehicle engine control, and more particularly, to a catalytic converter control system for oxygen storage management and control.
Increasingly stringent federal and state motor vehicle emissions standards require that specific emissions-related systems on a motor vehicle be controlled and optimized. These systems must be functioning as intended over the life of the vehicle, and if the systems have deteriorated or lose their functionality, the vehicle operator must be informed and the system repaired. For example, a catalytic converter of a motor vehicle is monitored because of its ability to reduce undesirable emissions in exhaust gases from the engine of the motor vehicle.
The performance of the catalytic converter depends upon the chemical compositions of the exhaust gases from the engine of the motor vehicle. Maintaining the feed-gas concentration to the catalytic converter close to stoichiometry maximizes catalytic converter efficiency. The oxygen storage capability of the catalytic converter determines the functional performance of the converter, which may also deteriorate over time due to factors such as engine misfire, a faulty oxygen sensor, poisoning or prolonged high-temperature operation. Such deteriorzatioin results in diminished capability to store the oxygen available in the exhaust gases. Active management and control of the amount of oxygen stored in the catalyst during motor vehicle operation helps lower pollutants from motor vehicle emissions.
Three-way catalytic converters are designed to have oxygen storage capability to improve their conversion efficiency. Oxygen storage/release is carried out by the precious-metal-assisted transition between Ce3+ and Ce4+ of Ceria compound added to the washcoat of the catalyst. The major storage/release reactions are shown below. 
Current engines have an on-board control system that applies one or more oxygen sensor outputs to control fuel/air flow rates. Emission control is accomplished by increasing catalyst loading. This results in adding more precious metal particles, thereby increasing the overall volume and cost of the catalytic converter.
A major drawback of current engine systems are that no known current engines employ active management of oxygen storage amount or oxygen storage capacity. Knowing the instantaneous oxygen storage amount is key to emission control. A further drawback is that catalysts can be saturated when too much oxygen is coming high-temperature exposure and poisoning due to the decreased surface area of the Ceria and the precious metal particles.
Accordingly, active oxygen storage management and control would improve emission control. An engine capable of predicting instantaneous oxygen storage amount is desired to overcome emission breakthroughs, increase catalytic converter efficiency, and generally reduce the overall size and cost of the catalytic converter.
The active oxygen storage management and control method and system according to the invention include sensing oxygen levels upstream and downstream of a catalytic converter for a fuel-injected engine of a motor vehicle. An engine control system predicts an oxygen consumption mass flow rate, and then determines an oxygen storage mass flow rate based on the sensed upstream and downstream oxygen levels and the predicted oxygen consumption mass flow rate. The oxygen storage mass flow rate is used to determine an instantaneous oxygen storage amount.
To determine the oxygen storage mass flow rate, the upstream and downstream oxygen levels are sensed and used to calculate upstream and downstream oxygen mass fractions, which are then used to determine a converter-in oxygen mass flow rate and a converter-out oxygen mass flow rate. Thus, the oxygen mass flow rate is preferably determined from converter-in mass flow rate, converter-out mass flow rate, and the predicted oxygen consumption mass flow rate.
Further, the upstream and downstream oxygen levels are preferably used to determine an upstream and downstream oxygen flow rate by determining an upstream and downstream lambda. In this manner, the determination of the upstream and downstream oxygen mass fractions are achieved by using the upstream or downstream lambda, respectively, as well as a set of reaction constants and a reaction fraction.
The method according to the invention is used to control exhaust emissions from a motor vehicle by predicting an instantaneous oxygen storage amount in the catalytic converter, determining a maximum oxygen storage capacity, and selecting a target percentage of the maximum oxygen storage amount. The motor vehicle engine performance is controlled so that the instantaneous oxygen storage amount is approximately the target percentage of the maximum oxygen storage amount. To accomplish this control, the instantaneous oxygen storage amount and the maximum oxygen storage amount are calculated as discussed above.
An engine control system according to the invention disposes oxygen sensors upstream and downstream from a catalytic converter. The engine control system monitors engine operating parameters including an output signal on the upstream and downstream oxygen sensors, determines an instantaneous oxygen storage amount based on the monitored sensor output signals, and controls engine operation to maintain the determined instantaneous oxygen storage amount in a predicted oxygen storage capacity. The engine control system monitors a plurality of engine control terms including a target instantaneous oxygen storage amount selected within a range from zero oxygen storage capacity to about a predicted maximum oxygen storage capacity.
The engine control system controls engine operation to maintain the instantaneous oxygen storage amount at approximately the target instantaneous oxygen storage amount. A plurality of fuel injectors receive a control signal from the engine control system to supply fuel to the engine at a rate where the instantaneous oxygen storage amount is approximately the target instantaneous oxygen storage amount.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.